Wide and thick steel plate for 600MPa-grade corrosion-resistant anti-fatigue marine tendon pipe and production method of wide and thick steel plate

Abstract

The invention discloses a wide and thick steel plate for a 600MPa-grade corrosion-resistant anti-fatigue marine tendon pipe and a production method of the wide and thick steel plate. According to the component design of the wide and thick steel plate, CEIIW is controlled to be 0.37%-0.42%, and CEPcm is controlled to be 0.14%-0.18%; the low-Nb and Mo-free design is adopted, the phase change temperature is increased, and phase change of polygonal ferrite is promoted; rE is fully utilized to exert the effects of solid solution, interface segregation and the like, grains are refined, the interface energy is reduced, and the corrosion resistance is improved; on the basis of component design, the production methods of low-temperature heating, rough rolling multi-stage thickness section high-temperature gradient deformation and low-temperature rolling, intermediate temperature-waiting blank rapid cooling after rough rolling is finished, finish rolling low-temperature deformation, multi-stage water cooling and the like are adopted to obtain a microstructure of polygonal ferrite, granular bainite and acicular ferrite; and the average deformation austenite height does not exceed 18 microns, and the proportion, the size and the distribution of each phase are ideally controlled, so that the method plays an important role in obtaining good comprehensive performance of the steel plate.

Description

Technical Field

[0001] The present invention belongs to the technical field of low alloy steel, and in particular relates to a 600MPa-grade thick-walled, high-toughness, corrosion-resistant, fatigue-resistant, and easily weldable wide and thick steel plate for marine tendon tubes with a thickness of ≥30mm, and a production method thereof, which is suitable for making high-performance marine platform tendon tubes; specifically, a 600MPa-grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes and a production method thereof. Background Art

[0002] As the demand for oil and natural gas continues to increase, the development of marine oil and gas resources has received increasing attention. According to analysis by international authoritative organizations, marine oil and gas resources will account for about 63% of the world's recoverable oil and gas reserves in the future, of which deep-sea oil and gas resources will account for 43%; the development of marine oil and gas resources has become the main economic growth point of the oil and gas industry. Therefore, it is urgent to develop key equipment and materials for marine, especially deep-sea oil and gas development.

[0003] Tendon tubes are core components of TLP and other offshore platforms, used to connect the upper buoy of the platform and the seabed anchoring system. The maximum water depth of application exceeds 1,500 meters. The service conditions are harsh, and they are subjected to the coupling of high-depth external pressure, fixed loads, marine environmental loads, operating loads and fluid static loads. They are also subject to long-term corrosion under marine and operating conditions. Therefore, the marine tendon tubes must have comprehensive properties such as high strength, high toughness, corrosion resistance, fatigue resistance and easy welding.

[0004] There have been some similar studies on steel for marine tendon tubes in the prior art, but there are still some technical defects that need to be solved; for example, patent CN109720514A "Tendons for tension leg floating wind power platform" provides a structure and design of telescopic tension tendons, but it does not involve tendon tube materials. Patent CN110106439 A "X65 hot-rolled steel plate for marine risers and preparation method thereof" provides an X65-grade marine riser steel plate, which uses a high content of Nb and Ni in the composition, resulting in high production and manufacturing costs. Patent CN116555670 A "A fatigue-resistant marine riser steel and preparation method thereof" provides a marine riser steel, which also has a high alloy content and requires the cumulative deformation of the last 2 to 3 passes of rough rolling to be greater than 50%. For wide and thick steel plates, industrialization is difficult to achieve and requires high equipment capabilities. Patent CN114763593A "Marine engineering steel with high humidity and heat atmospheric corrosion resistance and its manufacturing method" provides a marine engineering steel, which adopts high Ni and Cr content design and rolling + tempering process, with high production cost and long manufacturing cycle. Patent CN113075064A "A full-scale fatigue test method for tension leg platform tension tendon welded joint" provides a fatigue test method for tension tendon welded joint, but it does not involve the tendon tube material itself.

[0005] In summary, the existing technology has deficiencies in the research on wide and thick steel plates for marine tendons, especially high-performance steel for marine platform tendons with comprehensive technical characteristics such as thick walls, high toughness, corrosion resistance, fatigue resistance, and weldability, and urgent improvements are needed. Summary of the Invention

[0006] In order to overcome the defects of the above existing technology and solve the problem of matching comprehensive technical characteristics such as thick walls, high toughness, corrosion resistance, fatigue resistance, and weldability of wide and thick steel plates for marine tendons, the present invention provides a wide and thick steel plate for 600MPa-class corrosion-resistant and fatigue-resistant marine tendons and its production method to meet the technical requirements of high-performance steel for marine platform tendons.

[0007] In order to achieve the above invention purpose, the present invention provides a wide and thick steel plate for 600MPa-class corrosion-resistant and fatigue-resistant marine tendons. The chemical composition of the wide and thick steel plate in weight percentage is: C: 0.030% - 0.060%, Si: 0.20% - 0.45%, Mn: 1.40% - 1.65%, Nb: 0.010% - 0.035%, Ti: 0.008% - 0.025%, Ti / N ≥ 3.42, Ni: 0.01% - 0.15%, Cu: 0.01% - 0.15%, Cr: 0.20% - 0.50%, (Cr + Ni + Cu): 0.30% - 0.70%, RE: 0.003% - 0.008%, Al: 0.020% - 0.045%, Ca: 0.0015% - 0.0040%, Ca / S ≥ 1.6, N: 0.002% - 0.007%, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0012%, and the balance is iron and unavoidable impurities.

[0008] The CE of the wide and thick steel plate for 600MPa-class corrosion-resistant and fatigue-resistant marine tendons IIW is controlled within 0.37% - 0.42%, and CE Pcm is controlled within 0.14% - 0.18%;

[0009] Among them, CE IIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15;

[0010] CE Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B; where each element symbol represents the weight percentage of the corresponding element.

[0011] The thickness of the above-mentioned 600MPa grade corrosion-resistant and fatigue-resistant marine tendon steel plate is ≥30mm. In the composition, a low-Nb and Mo-free design is adopted to increase the phase transformation temperature, promote the transformation of polygonal ferrite, ensure its proportion in the microstructure, and at the same time improve the alloy economy. Make full use of RE to play roles such as solid solution and interfacial segregation, improve strength, refine grains, reduce interfacial energy, and improve corrosion resistance; and work together with Ca to play the roles of purifying molten steel and modifying and dispersing inclusions, reducing the adverse effects of inclusions on fatigue performance. By adding a small amount of Ni and Cu, the strength and toughness and corrosion resistance are improved; use inexpensive Cr and Mn elements to ensure strength and improve the economy of the product. In addition, by reducing the contents of P, S, H, and O and controlling the quality of continuous casting billets, etc., the toughness, corrosion resistance, and fatigue resistance are improved; combined with production processes such as smelting, heating, rolling, and cooling that match the alloy composition, the steel plate obtains comprehensive technical characteristics such as high strength, high toughness, corrosion resistance, fatigue resistance, and weldability, and an ideal microstructure.

[0012] Reasons for the composition design of the present invention:

[0013] C is a basic element for improving strength, with obvious effects on improving hardenability and tensile strength, and is also beneficial to the control of the yield ratio; however, too high a carbon content is unfavorable for plasticity, toughness, weldability, corrosion resistance, etc.; in the present invention, the C content is controlled at 0.030% - 0.060%.

[0014] Si can improve hardenability and strength. At the same time, too high an Si content will increase M / A in the structure, reducing toughness and plasticity. In the present invention, its suitable content range is 0.20% - 0.45%.

[0015] Mn can effectively improve strength and hardenability. At the same time, Mn can also reduce the phase transformation temperature, which is beneficial to grain refinement; moreover, the Mn element is inexpensive and can improve the economy of the product; but too high a manganese content is prone to induce segregation, resulting in a reduction in corrosion resistance and fatigue resistance, etc. In the present invention, the Mn content is controlled at 1.40% - 1.65%.

[0016] Nb has a grain refinement effect, can improve strength and toughness, and can also form fine Nb(C, N) precipitates under appropriate processes to play the role of precipitation strengthening; but too high an Nb content, on the one hand, requires increasing the heating temperature of the continuous casting billet to ensure the solid solution effect, increasing energy consumption; and it will inhibit the transformation of austenite to polygonal ferrite, increasing the control difficulty of polygonal ferrite in the microstructure; therefore, the Nb content is controlled at 0.010% - 0.035%.

[0017] Ti has the effect of fixing nitrogen, easily forms precipitation phases of Ti(C, N) with a relatively high solution temperature, inhibits the grain growth of austenite under high-temperature conditions; at the same time, Ti can also refine the welding structure, improve the toughness of the heat-affected zone after welding; and has the effect of fixing oxygen; however, if the Ti content is too high, the size of the precipitates will increase and the beneficial effects will decrease. In the present invention, the Ti content is controlled to be 0.008% - 0.025%, and Ti / N ≥ 3.42.

[0018] Ni has a solution strengthening effect, which is beneficial to improving toughness; it can reduce the critical cooling rate and delay the pearlite transformation; it can also reduce Cu embrittlement and improve corrosion resistance; however, the price of Ni is relatively high, and adding too much is not beneficial to economy; therefore, in the present invention, the Ni content is controlled to be 0.01% - 0.15%.

[0019] Cu improves hardenability, increases the proportion and hardness of the hard-phase structure, improves the tensile strength, and is beneficial to corrosion resistance at the same time, but too high a Cu content is not beneficial to toughness. In the present invention, the Cu content is controlled to be 0.01% - 0.15%.

[0020] Cr can increase hardenability, improve the tensile strength, has a weak inhibition on the transformation of austenite to polygonal ferrite, is beneficial to increasing the "hardness difference" between soft / hard phases in the microstructure, and is beneficial to the control of the yield ratio; moreover, as an inexpensive element, Cr can replace precious alloy elements such as Mo, Ni, and Cu, effectively reducing the cost; however, too high a Cr content will increase the sensitivity to welding cracks. Therefore, in the present invention, the Cr content is controlled to be 0.20% - 0.50%.

[0021] (Cr + Ni + Cu) being controlled to be 0.30% - 0.70% can ensure hardenability, strengthening effect, and is beneficial to phase transformation and microstructure control at the same time.

[0022] RE: In the present invention, the RE element can effectively inhibit the diffusion of elements such as C, control phase transformation, and promote medium-temperature tissue transformation; it is beneficial to increasing strength under solution conditions; when segregating at interfaces such as grain boundaries and phase boundaries, it will reduce the interface energy and corrosion sensitivity; it can also improve the density of the rust layer and reduce the corrosion rate. In addition, during the smelting process, it is beneficial to the reduction, dispersion, and spheroidization of inclusions, improving the quality of the continuous casting billet and reducing the adverse effects of inclusions on fatigue performance. In the present invention, the RE content is controlled to be 0.003% - 0.008%.

[0023] Al has a strong affinity with O and N and is a deoxidizing element, but too high an Al content will promote the increase of inclusions. In the present invention, the Al content is controlled to be 0.020% - 0.045%.

[0024] Ca and Ca / S can promote the modification and spheroidization of inclusions, effectively improving corrosion resistance, toughness, and fatigue performance. In the present invention, the Ca content is controlled to be 0.0015% - 0.0040%, and Ca / S ≥ 1.6.

[0025] N can form fine precipitates with Nb and Ti, playing roles such as strengthening, grain refinement, and hydrogen trapping. However, too high N content deteriorates toughness and may also cause defects in the steel plate. In the present invention, the N content is controlled within 0.002% - 0.007%.

[0026] P and S are harmful impurity elements in the present invention; P causes a decrease in toughness, and in the present invention, P is controlled to be ≤0.010%; an increase in S content promotes the formation and growth of inclusions, destroys the matrix continuity, and leads to a decline in fatigue and corrosion resistance. Therefore, S is controlled to be ≤0.002%.

[0027] An increase in H and O contents leads to a decrease in toughness and an increase in inclusions, affecting corrosion resistance, fatigue performance, etc. Therefore, in the present invention, H is controlled to be ≤0.00015% and O is controlled to be ≤0.0012%.

[0028] In the composition design of the heavy and wide steel plate for 600MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes in this technical solution, the CE IIW is controlled within 0.37% - 0.42%, and the CE Pcm is controlled within 0.14% - 0.18%. It can not only meet the requirements of the strength and toughness of the steel plate but also reduce the tendency of welding cracking, making the steel plate have good weldability.

[0029] A production method of the heavy and wide steel plate for 600MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes as described above. The production method includes the following technological steps: converter smelting, secondary refining, continuous casting, rolling, and cooling;

[0030] Among them, the tapping temperature of the converter is ≤1640°C and C is ≤0.040%;

[0031] After refining and deoxidation, Ti is added first, and then RE is added; the holding time before the molten steel is fed into the machine is ≥10 min, the superheat of the continuous casting billet during pouring is 20°C - 45°C, the average residence time of the molten steel in the tundish during pouring is ≥380 s, and the dynamic soft reduction of the billet is ≥4 mm;

[0032] The continuous casting billet is heated in multiple stages including pre - heating, heating, and soaking. The total heating time is 1.1 - 1.8 min / mm, and the tapping temperature is 1120°C - 1170°C;

[0033] The rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The starting rolling temperature of rough rolling is 1080°C - 1140°C, and the final rolling temperature of rough rolling is 980°C - 1030°C;

[0034] The deformation rate in the finish rolling stage is 60% - 75%, the starting rolling temperature of finish rolling is 780°C - 830°C, and the final rolling temperature of finish rolling is 740°C - 770°C;

[0035] The rolled steel plate is subjected to two-stage cooling after pre-straightening.

[0036] In the above technical solution, further, slag is blocked during tapping from the converter, the thickness of the slag layer is ≤ 35 mm, lime and fluorite are added to make the top slag according to the mass ratio of 4 / 1 to 5 / 1, and the weight percentage of FeO + MnO in the slag is controlled to be ≤ 1%.

[0037] Further, the continuous casting adopts a constant casting speed, the casting speed control range is 0.6 - 1.2 m / min, the central segregation of the continuous casting billet is ≤ C0.5 level, the central porosity is ≤ 0.5 level, and the inclusions of types A / B / C / D are controlled within level 1.

[0038] Low-carbon, low-temperature, and slag-blocking tapping from the converter can effectively control the carbon content of the final product, ensure the dephosphorization effect, and reduce rephosphorization and resulfurization; making white slag and controlling FeO + MnO in the slag can ensure the reduction ability of the slag, fully desulfurize, reduce inclusions, and improve cleanliness; the addition sequence of Ti and RE after refining deoxidation can more effectively improve the recovery rate and efficiency of the corresponding elements; the control of the ladle calmness before the molten steel is fed into the machine, the pouring superheat, and the residence time in the tundish can equalize the temperature of the molten steel, effectively promote the floating and removal of inclusions; the dynamic soft reduction and the control of the continuous casting billet casting speed can effectively improve the quality of the casting billet, reduce defects such as cracks and segregation, and the control of central segregation, central porosity, and inclusions is an effective guarantee for the quality of the continuous casting billet and the performance of the steel plate.

[0039] In the above technical solution, further, the continuous casting billet is subjected to multi-stage heating including preheating, heating, and soaking, the total heating time is 1.1 - 1.8 min / mm, and the tapping temperature is 1120°C - 1170°C. The multi-stage heating of the continuous casting billet and the control of the total heating time are beneficial to improving the heating efficiency and uniformity; since the Nb content in the present invention is low, low-temperature heating and tapping can meet the need for element solid solution, and at the same time, it can effectively reduce the austenite grain size, and is more conducive to reducing the rough rolling temperature, reducing the rolling time in the rough rolling stage, and realizing high-efficiency low-temperature rolling.

[0040] In the above technical solution, further, in the three stages of the first rough rolling stage, intermediate cooling, and the second rough rolling stage of rough rolling, the last 2-3 passes of the first rough rolling stage, intermediate cooling, and the second rough rolling stage all adopt rapid spray water cooling; the starting temperature of the second rough rolling stage is below 1050 °C, the total deformation rate ≥ 30%, the deformation rate of each pass ≥ 15% and increases gradually from pass to pass, and the rough rolling speed is 1.0 m / s - 1.8 m / s. The key of rough rolling in this technical solution is to adopt the process of low-temperature rolling + high temperature gradient deformation of the thickness section. Due to the low Nb content of the present invention, the austenite recrystallization temperature is reduced; therefore, low-temperature rolling and other methods are adopted in the rough rolling stage to recrystallize austenite grains and effectively inhibit grain growth; through multi-stage rapid cooling, the temperature gradient of the thickness section is significantly increased, and the low-temperature and low-speed rolling in the second rough rolling stage is combined to promote the penetration of rolling deformation to the thickness center of the slab, refine the structure near the thickness center, and improve the uniformity of the steel plate structure performance; the gradually increasing deformation rate in the second rough rolling stage can promote the full recrystallization of austenite.

[0041] In the above technical solution, further, the deformation rate in the finish rolling stage is 60% - 70%. After rough rolling, the intermediate waiting billet is rapidly cooled to 840 °C - 880 °C, and the average cooling speed ≥ 2 °C / s. Then, it is waited until the finish rolling starting temperature. The finish rolling starting temperature is 780 °C - 830 °C, the finish rolling final temperature is 740 °C - 770 °C. After the rolled steel plate is pre-straightened, it is cooled in two stages. The starting water cooling temperature is 700 °C - 740 °C, the water cooling end temperature is 250 °C - 380 °C. When water cooling, the water volume of the first 5 - 7 sets of upper headers is 400 - 550 L / m 2 ·min, and the water volume of the remaining upper headers is 200 - 350 L / m 2 ·min. The deformation rate in the finish rolling stage can ensure the deformation and flattening of austenite in the non-recrystallized zone; the rapid cooling of the intermediate waiting billet after rough rolling can quickly reduce the temperature to 30 °C - 70 °C higher than the finish rolling starting temperature, effectively inhibiting the growth of austenite; the low-temperature rolling adopted in the finish rolling stage is beneficial to the formation of substructures in the microstructure and the accumulation of deformation energy, promoting phase transformation nucleation and refining grains; the pre-straightening of the rolled steel plate is beneficial to improving the water cooling uniformity and ensuring the plate shape of the steel plate; the control of the starting water cooling temperature can ensure the formation of part of the polygonal ferrite soft phase structure before accelerating water cooling; adopting a lower final cooling temperature can promote the formation of a high-hardness structure mainly composed of granular bainite and acicular ferrite; adopting the segmented water cooling process with fast first and slow later can, on the one hand, increase the cooling speed in the high-temperature section and inhibit high-temperature phase transformation. At the same time, the smaller cooling water volume in the low-temperature section can reduce the internal stress and improve the plate shape after cooling.

[0042] The wide and thick steel plate for 600 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared by the above - mentioned production method has a microstructure of polygonal ferrite + granular bainite + acicular ferrite. Among them, the volume percentage of polygonal ferrite is 35% - 75%, and the average height of deformed austenite does not exceed 18 μm. The steel plate has comprehensive technical characteristics such as high strength, high toughness, corrosion resistance, fatigue resistance and easy weldability, and can meet the requirements for manufacturing high - performance marine platform tendon pipes.

[0043] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0044] ① In the composition of the present invention, a low - Nb and Mo - free design is adopted to increase the phase - transformation temperature, promote the phase - transformation of polygonal ferrite, ensure its proportion in the microstructure, and at the same time improve the alloy economy. Make full use of RE to play roles such as solid solution and interfacial segregation, improve strength, refine grains, reduce interfacial energy, and improve corrosion resistance. Moreover, RE and Ca act together to purify the molten steel and modify and disperse inclusions, reducing the adverse effects of inclusions on fatigue performance. By adding a small amount of Ni and Cu, the strength and toughness and corrosion resistance are improved. Use inexpensive Cr and Mn elements to ensure strength and improve the economy of the product. In addition, by reducing the contents of P, S, H, and O and controlling the quality of continuous casting billets, etc., the toughness, corrosion resistance and fatigue resistance are improved; combined with production processes such as smelting, heating, rolling and cooling that match the alloy composition, the problem of matching the comprehensive technical characteristics of high strength, high toughness, corrosion resistance, fatigue resistance and easy weldability of the wide and thick steel plate for marine tendon pipes is solved.

[0045] ② Based on the composition design of the present invention, production methods such as low - temperature heating, multi - stage thickness - section high - temperature - gradient deformation + low - temperature rolling in rough rolling, rapid cooling of the intermediate waiting - temperature billet after rough rolling, low - temperature deformation in finish rolling and multi - stage water cooling are adopted to obtain a microstructure of polygonal ferrite + granular bainite + acicular ferrite, with the average height of deformed austenite not exceeding 18 μm. The proportion, size and distribution of each phase are ideally controlled, which plays an important role in obtaining good comprehensive properties of the steel plate.

[0046] ③ The thickness of the wide and thick steel plate for 600 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes of the present invention is ≥30 mm. The transverse yield strength can reach 500 - 570 MPa, the transverse tensile strength reaches 610 - 690 MPa, the transverse yield - strength ratio < 0.87, the average - value of transverse impact energy at - 60 °C ≥280 J, the average - value of transverse impact energy in the welding heat - affected zone at - 20 °C ≥200 J, the transverse CTOD at - 20 °C ≥0.7 mm, and the transverse DWTT shear area at - 20 °C ≥85%; the longitudinal yield strength can reach 485 - 550 MPa, the longitudinal tensile strength reaches 600 - 670 MPa, the longitudinal yield - strength ratio < 0.86, 10 7The weekly fatigue strength ≥ 330 MPa; the anti-SSCC corrosion performance meets the requirement that no fracture occurs after being soaked in saturated H 2 S solution for 720 hours under 72% stress loading condition and no visible crack is observed under 10 times magnification; the fabricated marine tendon pipe meets the requirement of 600 MPa grade. Brief Description of the Drawings

[0047] Figure 1 It is the microstructure diagram of the wide and thick steel plate for 600 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipe prepared in Example 1. Detailed Implementation Modes

[0048] The present invention will be further described below in conjunction with specific embodiments, but the present invention is not limited in any way. To avoid repetition, in the following embodiments, the raw materials are all commercially available products unless otherwise specified, and the methods used are all conventional methods unless otherwise specified.

[0049] For the wide and thick steel plate for 600 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipe, the chemical composition of the wide and thick steel plate by weight percentage is C: 0.030% - 0.060%, Si: 0.20% - 0.45%, Mn: 1.40% - 1.65%, Nb: 0.010% - 0.035%, Ti: 0.008% - 0.025%, Ti / N ≥ 3.42, Ni: 0.01% - 0.15%, Cu: 0.01% - 0.15%, Cr: 0.20% - 0.50%, (Cr + Ni + Cu): 0.30% - 0.70%, RE: 0.003% - 0.008%, Al: 0.020% - 0.045%, Ca: 0.0015% - 0.0040%, Ca / S ≥ 1.6, N: 0.002% - 0.007%, P ≤ 0.010%, S ≤ 0.002%, H ≤ 0.00015%, O ≤ 0.0012%, and the balance is iron and inevitable impurities.

[0050] The CE of the wide and thick steel plate for 600 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipe IIW is controlled within 0.37% - 0.42%, and the CE Pcm is controlled within 0.14% - 0.18%.

[0051] Among them, CE IIW = C + Mn / 6 + (Cr + Mo + V) / 5 + (Ni + Cu) / 15;

[0052] CE Pcm = C + Si / 30 + (Mn + Cu + Cr) / 20 + Ni / 60 + Mo / 15 + V / 10 + 5B; in the formula, each element symbol represents the weight percentage of the corresponding element.

[0053] A production method of a wide and thick steel plate for 600MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes, the production method includes the following technological steps: converter smelting, secondary refining, continuous casting, rolling, and cooling, etc.;

[0054] Among them, the tapping temperature of the converter ≤ 1640°C, C ≤ 0.040%;

[0055] After refining and deoxidation, Ti is added first, and then RE is added; the calming time of the molten steel before being fed into the machine ≥ 10min, the superheat of the continuous casting billet during pouring is 20°C - 45°C, the average residence time of the molten steel in the tundish during pouring ≥ 380s, and the dynamic soft reduction of the billet ≥ 4mm;

[0056] The continuous casting billet is heated in multiple stages including pre - heating, heating, and soaking, with a total heating time of 1.1 - 1.8min / mm, and the tapping temperature is 1120°C - 1170°C;

[0057] Rough rolling includes three stages: rough rolling stage 1, intermediate cooling, and rough rolling stage 2. The starting rolling temperature of rough rolling is 1080°C - 1140°C, and the final rolling temperature of rough rolling is 980°C - 1030°C. Among them, the last 2 - 3 passes of rough rolling stage 1, intermediate cooling, and rough rolling stage 2 all adopt rapid spray water cooling;

[0058] The deformation rate in the finish - rolling stage is 60% - 75%. After rough rolling, the intermediate waiting - temperature billet is rapidly cooled to 840°C - 880°C, with an average cooling rate ≥ 2°C / s. Then, it is waited - temperature to the finish - rolling starting temperature. The finish - rolling starting temperature is 780°C - 830°C, and the finish - rolling final temperature is 740°C - 770°C;

[0059] After pre - straightening the rolled steel plate, two - stage cooling is carried out.

[0060] For the parts not described in the following embodiments, they are the same as the description content of the above - mentioned specific implementation manners.

[0061] Embodiment

[0062] For the wide and thick steel plate for 600MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes and its production method, the chemical compositions of the wide and thick steel plates in Embodiments 1 - 8 are shown in Table 1.

[0063] Table 1 Chemical composition table of the wide and thick steel plates in Embodiments 1 - 8 wt%

[0064]

[0065]

[0066] For Examples 1 - 8, the smelting and refining process parameters of the heavy plate production method are shown in Table 2. The tapping temperature of the converter is ≤1640°C, and C is ≤0.040%. Tapping with slag blocking is carried out, the thickness of the slag layer is ≤35 mm, lime and fluorite are added in a mass ratio of 4 / 1 - 5 / 1 to make the top slag, and the weight percentage of FeO + MnO in the slag is controlled to be ≤1%.

[0067] Table 2 Smelting and refining process parameters of Examples 1 - 8

[0068]

[0069] For Examples 1 - 8, the continuous casting process parameters of the heavy plate production method are shown in Table 3. The calming time of the molten steel before entering the machine is ≥10 min, the superheat of the continuous casting billet during pouring is 20°C - 45°C, the average residence time of the molten steel in the tundish during pouring is ≥380 s, and the dynamic soft reduction of the billet is ≥4 mm. Continuous casting is carried out at a constant casting speed, and the casting speed control range is 0.6 - 1.2 m / min. The center segregation of the continuous casting billet is ≤C0.5 level, the center porosity is ≤0.5 level, and the control of A / B / C / D type inclusions is within level 1.

[0070] Table 3 Continuous casting process parameters of Examples 1 - 8

[0071]

[0072]

[0073] For Examples 1 - 8, the control parameters of the continuous casting billet heating and rough rolling process of the heavy plate production method are shown in Table 4. The continuous casting billet is heated in multiple stages including preheating, heating, and soaking, with a total heating time of 1.1 - 1.8 min / mm and an out - furnace temperature of 1120°C - 1170°C. The rough rolling starting temperature is 1080°C - 1140°C, and the rough rolling finishing temperature is 980°C - 1030°C. The starting temperature of the second stage of rough rolling is below 1050°C, the total reduction rate is ≥30%, the reduction rate of each pass is ≥15% and increases gradually, and the rough rolling speed is 1.0 m / s - 1.8 m / s.

[0074] Table 4 Continuous casting billet heating and rough rolling process parameters of Examples 1 - 8

[0075]

[0076] The finishing rolling and cooling process parameters of the production methods for wide and heavy plates in Examples 1 to 8 are shown in Table 5. In the finishing rolling stage, the deformation rate is 60% - 75%. After rough rolling, the intermediate waiting billet is rapidly cooled to 840°C - 880°C, with an average cooling rate ≥ 2°C / s. Then, it is waited until the finishing rolling starting temperature. The finishing rolling starting temperature is 780°C - 830°C, the finishing rolling ending temperature is 740°C - 770°C. After the rolled plate is pre-straightened, it undergoes two-stage cooling. The starting water cooling temperature is 700°C - 740°C, the ending water cooling temperature is 250°C - 380°C. During water cooling, the water volume of the first 5 - 7 groups of upper headers is 400 - 550 L / m 2 ·min, and the water volume of the remaining upper headers is 200 - 350 L / m 2 ·min.

[0077] Table 5 Finishing rolling and cooling processes of the examples

[0078]

[0079] The statistical results of the microstructures of the wide and heavy plates for 600 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared in Examples 1 to 8 are shown in Table 6. The microstructure of the wide and heavy plate is polygonal ferrite + granular bainite + acicular ferrite (such as the microstructure of the product prepared in Example 1 shown Figure 1 ). Among them, the volume percentage of polygonal ferrite is 35% - 75%, and the average height of deformed austenite does not exceed 18 μm.

[0080] Table 6 Statistical results of the microstructures of Examples 1 to 8

[0081] Embodiment Volume percentage of polygonal ferrite / % Average height of deformed austenite / μm 1 43 14.3 2 44 13.5 3 35 13.9 4 62 13.3 5 50 14.0 6 61 14.5 7 68 14.8 8 47 13.8

[0082] The mechanical property test results of the wide and heavy plates for 600 MPa - grade corrosion - resistant and fatigue - resistant marine tendon pipes prepared in Examples 1 to 8 are shown in Table 7. The thickness of the wide and heavy plate is ≥ 30 mm, the transverse yield strength is 500 - 570 MPa, the transverse tensile strength is 610 - 690 MPa, the transverse yield ratio < 0.87, the average - 60°C transverse impact energy ≥ 280 J, the average - 20°C transverse impact energy of the heat - affected zone of welding ≥ 200 J, - 20°C transverse CTOD ≥ 0.7 mm, - 20°C transverse DWTT shear area ≥ 85%; the longitudinal yield strength is 485 - 550 MPa, the longitudinal tensile strength is 600 - 670 MPa, the longitudinal yield ratio < 0.86, 10 7 cycle fatigue strength ≥ 330 MPa.

[0083] Table 7 Mechanical property test results of the products prepared in Examples 1 to 8

[0084]

[0085] The corrosion resistance test results of the 600 MPa grade corrosion-resistant and fatigue-resistant marine tendon pipes made of the wide and thick steel plates prepared in Examples 1 to 8 are shown in Table 8. The anti-SSCC corrosion performance meets the requirement that no fracture occurs after being soaked in saturated H 2 S solution under 72% stress loading condition for 720 hours and no visible cracks are observed under 10 times magnification.

[0086] Table 8 Corrosion resistance test results of the products prepared in Examples 1 to 8

[0087]

[0088] It can be illustrated by Examples 1 to 8 that in the composition of the present invention, a low-Nb and Mo-free design is adopted to increase the phase transformation temperature, promote the transformation of polygonal ferrite, and ensure its proportion in the microstructure. At the same time, the alloy economy is improved; the functions of solid solution and interfacial segregation of RE are fully utilized to increase the strength, refine the grains, reduce the interfacial energy, and improve the corrosion resistance. Moreover, in combination with Ca, it plays the roles of purifying the molten steel, modifying and dispersing inclusions, and reducing the adverse effects of inclusions on the fatigue performance; by adding a small amount of Ni and Cu, the strength, toughness and corrosion resistance are improved. On the basis of the composition design, production methods such as low-temperature heating, multi-stage thickness-section high-temperature gradient deformation + low-temperature rolling in rough rolling, rapid intermediate waiting billet after rough rolling, low-temperature deformation in finish rolling, and multi-stage water cooling are adopted to obtain a microstructure of polygonal ferrite + granular bainite + acicular ferrite. The average height of deformed austenite does not exceed 18 μm, and the proportion, size and distribution of each phase are ideally controlled, which plays an important role in obtaining good comprehensive properties of the steel plate.

[0089] For any person skilled in the art, without departing from the scope of the technical solution of the present invention, many possible changes and modifications can be made to the technical solution of the present invention by using the technical content disclosed above, or modified into equivalent embodiments with equivalent changes. Therefore, any simple modification, equivalent change and modification made to the above embodiments according to the technical essence of the present invention without departing from the content of the technical solution of the present invention shall still fall within the scope of protection of the technical solution of the present invention.

Claims

1. 600MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes, characterized by: The chemical composition weight percentage of the wide and thick steel plate is C: 0.030% to 0.060%, Si: 0.20% to 0.45%, Mn: 1.40% to 1.65%, Nb: 0.010% to 0.035%, Ti: 0.008% to 0.025%, Ti / N ≥ 3.42, Ni: 0.01% to 0.15%, Cu: 0.01% to 0.15%, Cr: 0.20% to 0.50%, (Cr+Ni+Cu): 0.30%~0.70%, RE: 0.003%~0.008%, Al: 0.020%~0.045%, Ca: 0.0015%~0.0040%, Ca / S≥1.6, N: 0.002%~0.007%, P≤0.010%, S≤0.002%, H≤0.00015%, O≤0.0012%, the balance is iron and unavoidable impurities.

2. The 600MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes according to claim 1 is characterized in that: The wide and thick steel plate CE for marine tendon tube IIW Controlled at 0.37%~0.42%, CE Pcm Controlled at 0.14% to 0.18%; Among them, CE IIW =C+Mn / 6+(Cr+Mo+V) / 5+(Ni+Cu) / 15; CE Pcm =C+Si / 30+(Mn+Cu+Cr) / 20+Ni / 60+Mo / 15+V / 10+5B; wherein the symbol of each element represents the weight percentage of the corresponding element.

3. The 600MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes according to claim 1 is characterized in that: The thickness of the wide and thick steel plate is ≥30mm, the transverse yield strength is 500-570MPa, the transverse tensile strength is 610-690MPa, the transverse yield strength ratio is <0.87, the average transverse impact energy at -60°C is ≥280J, the average transverse impact energy at -20°C of the welding heat affected zone is ≥200J, the transverse CTOD at -20°C is ≥0.7mm, and the transverse DWTT shear area at -20°C is ≥85%; the longitudinal yield strength is 485-550MPa, the longitudinal tensile strength is 600-670MPa, the longitudinal yield strength ratio is <0.86, 10 7 The cyclic fatigue strength is ≥330MPa; the SSCC corrosion resistance meets the requirements of no fracture after 720 hours of immersion in saturated H2S solution under 72% stress loading conditions and no visible cracks under 10 times magnification observation.

4. The 600MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes according to claim 1 is characterized in that: The microstructure of the wide and thick steel plate is polygonal ferrite+granular bainite+acicular ferrite, wherein the volume percentage of polygonal ferrite is 35% to 75%, and the average height of deformed austenite does not exceed 18 μm.

5. A method for producing a 600MPa grade corrosion-resistant and fatigue-resistant wide and thick steel plate for marine tendon tubes as claimed in any one of claims 1 to 4, characterized in that: The production method comprises the following process steps: converter smelting, refining outside the furnace, continuous casting, rolling and cooling; Among them, the converter tapping temperature is ≤1640℃, C≤0.040%; After refining and deoxidation, Ti is added first, and then RE is added; the cooling time of molten steel before loading on the machine is ≥10min, the pouring superheat of continuous casting billet is 20℃~45℃, the average residence time of molten steel in the tundish during pouring is ≥380s, and the dynamic soft reduction of the casting billet is ≥4mm; The continuous casting billet adopts multi-stage heating of preheating, heating and soaking, with a total heating time of 1.1-1.8min / mm and a furnace temperature of 1120℃-1170℃; Rough rolling includes three stages: rough rolling stage 1, intermediate cooling and rough rolling stage 2. The starting temperature of rough rolling is 1080℃~1140℃, and the final temperature of rough rolling is 980℃~1030℃. The last 2~3 passes of rough rolling stage 1, intermediate cooling and rough rolling stage 2 are all cooled by rapid spray water. The deformation rate in the finishing rolling stage is 60% to 75%. After the rough rolling is completed, the intermediate warm billet is quickly cooled to 840°C to 880°C, with an average cooling rate of ≥2°C / s. Then, the billet is heated to the finishing rolling start temperature, the finishing rolling start temperature is 780°C to 830°C, and the finishing rolling final rolling temperature is 740°C to 770°C. The rolled steel plate is pre-straightened and then cooled in two stages.

6. The production method according to claim 5, characterized in that The converter is slag-blocking for tapping, with a slag layer thickness of ≤35mm. Lime and fluorite are added in a mass ratio of 4 / 1 to 5 / 1 to form top slag, and the weight percentage of FeO+MnO in the slag is controlled to be ≤1%.

7. The production method according to claim 5, characterized in that: The continuous casting adopts a constant pulling speed, the pulling speed control range is 0.6-1.2 m / min, the center segregation of the continuous casting billet is ≤C0.5 level, the center looseness is ≤0.5 level, and A / B / C / D type inclusions are controlled within 1 level.

8. The production method according to claim 5, characterized in that: The starting temperature of the second stage of rough rolling is below 1050° C., the total deformation rate is ≥30%, the deformation rate of each pass is ≥15% and increases gradually from pass to pass, and the rough rolling speed is 1.0 m / s to 1.8 m / s.

9. The production method according to claim 5, characterized in that: The water cooling temperature at the start of the two-stage cooling is 700°C to 740°C, and the water cooling end temperature is 250°C to 380°C; the water volume of the first 5 to 7 groups of upper headers during water cooling is 400 to 550 L / m 2 ·min, the water volume of other upper headers is 200~350L / m 2 ·min.

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